OLD RED SANDSTONE VOLCANIC ROCKS OF SHETLAND. 365 



Vaila Sound and Grating Voe on the south side of the axis ; but a large portion 

 of the area on this side is occupied by a great sheet of intrusive granite, which 

 will be referred to in a subsequent paragraph. By means of two powerful 

 faults, the altered Old Red strata are brought into conjunction with the meta- 

 morphic series on the east and north sides, and hence the unconformable relation 

 between the two is nowhere visible. A line drawn from a point not far to the 

 east of Aith Ness in Aithsting, southwards by Bixetter and Symbister Church 

 in Selie Voe, Sandsting, marks the course of the great north and south fault 

 bounding the area on the east. On the north side the fault runs from a point 

 west of Aith Ness in Aithsting, south-west by Sonso Ness, thence by Brindister, 

 Burrafirth, to Snarra Voe and Sandness Hill. Over a great part of this penin- 

 sular tract the beds consist of grey and blue indurated sandstones or grey wackes 

 with green and pale shales. The sandstones are abundantly traversed with 

 joints, which are frequently coated with peroxide of iron, and in places they 

 have a marked schistose character. Sometimes the sandstones are converted 

 into genuine quartzites, and the shales interbedded with them are distinctly 

 cleaved. The plant remains which we found at various points on the moors 

 between Walls and Sandness Hill occur in green and blue jointed sandstones 

 weathering with a yellowish or pale white crust. At certain localities the beds 

 are distinctly conglomeratic, especially on the rocky hills overlooking the head 

 of Snarra Voe and West Burrafirth Voe. Characterised by massive bedding 

 and containing more or less rounded pebbles of quartz, quartzites and various 

 metamorphic rocks, they remind one of the thick-bedcled conglomeratic sand- 

 stones at Lerwick on the eastern seaboard. Indeed, after several extensive 

 traverses we came to the conclusion that much of the altered series west of 

 Weisdale is the counterpart of the Lerwick series. The exact position of the 

 latter in the order of succession which we established on the eastern seaboard 

 will be readily seen from the following table : — 



5. Flaggy series of Bressay and Noss, consisting of alternations of 

 sandstones, flags and shales. At the base of Noss Head (577 feet) 

 there is a zone of dark calcareous shale with limestone nodules, 

 which has a striking resemblance to the well-known fish-bed of the 

 Moray Firth basin. 



4. Lerwick series, consisting of massive false-bedded sandstones, which 

 throughout are markedly conglomeratic. 



3. Rovey Head conglomerates. 



2. Brenista series, consisting of well-bedded red flags. 



1. Basement breccia. 



If we are right in inferring from the resemblance in lithological characters 

 i and the identity of the plant remains, that the altered strata west of Weisdale 



